Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level

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1 Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level * * CHEMISTRY 9701/35 Paper 3 Advanced Practical Skills 1 May/June hours Candidates answer on the Question Paper. Additional Materials: As listed in the Confi dential Instructions READ THESE INSTRUCTIONS FIRST Write your Centre number, candidate number and name on all the work you hand in. Give details of the practical session and laboratory where appropriate, in the boxes provided. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fl uid. DO NOT WRITE IN ANY BARCODES. Answer all questions. Electronic calculators may be used. You may lose marks if you do not show your working or if you do not use appropriate units. Use of a Data Booklet is unnecessary. Session Qualitative Analysis Notes are printed on pages 14 and 15. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. Laboratory For Examiner s Use Total This document consists of 13 printed pages and 3 blank pages. IB15 06_9701_35/5RP [Turn over

2 2 1 In this experiment you will determine the formula of iron(iii) ammonium sulfate, FeNH 4 (SO 4 ) 2.xH 2 O, where x is the number of molecules of water of crystallisation. A known mass of this iron(iii) compound reacted with excess acidifi ed potassium iodide to produce iodine. You will determine the amount of iodine produced by titrating the mixture with sodium thiosulfate. FA 1 is mol dm 3 sodium thiosulfate, Na 2 S 2 O 3. FA 2 is a solution of iodine, I 2, produced as outlined in the paragraph above. starch indicator (a) Method Diluting FA 1 Pipette 25.0 cm 3 of FA 1 into the 250 cm 3 volumetric (graduated) flask. Make the solution up to the mark using distilled water. Shake the flask to mix the solution thoroughly before using it for your titrations. Label this diluted solution of sodium thiosulfate FA 3. Rinse the pipette with distilled water. Keep FA 1 for use in Question 3. Titration Fill the burette with FA 3. Use the pipette to transfer 25.0 cm 3 of FA 2 into a conical flask. Add FA 3 from the burette into the conical flask until the mixture becomes pale yellow. Then add 10 drops of starch indicator to give a blue-black colour. Continue adding FA 3 until this blue-black colour disappears. This is the end-point of the titration. Perform a rough titration and record your burette readings in the space below. The rough titre is... cm 3. Carry out as many accurate titrations as you think necessary to obtain consistent results. Make sure any recorded results show the precision of your practical work. Record in a suitable table below, all of your burette readings and the volume of FA 3 added in each accurate titration. I II III IV V VI VII [7]

3 3 (b) From your accurate titration results, obtain a suitable value to be used in your calculations. Show clearly how you obtained this value cm 3 of FA 2 required... cm 3 of FA 3. [1] (c) Calculations Show your working and appropriate signifi cant fi gures in the fi nal answer to each step of your calculations. (i) Using information on page 2, calculate the concentration, in mol dm 3, of sodium thiosulfate in FA 3. concentration of Na 2 S 2 O 3 in FA 3 =... mol dm 3 (ii) Calculate the number of moles of sodium thiosulfate present in the volume of FA 3 calculated in (b). moles of Na 2 S 2 O 3 =... mol (iii) Use the equation below to calculate the number of moles of iodine that reacted with the sodium thiosulfate in (ii). I 2 + 2Na 2 S 2 O 3 2NaI + Na 2 S 4 O 6 (iv) Calculate the concentration of I 2, in mol dm 3, in FA 2. moles of I 2 =... mol concentration of I 2 =... mol dm 3 [Turn over

4 4 (v) The iodine in FA 2 was produced by the reaction of iron(iii) ions with excess potassium iodide. Balance the equation for this reaction.... Fe I... Fe I 2 Use your answer to (iv) and this equation to calculate the number of moles of iron(iii) ions that reacted to produce the iodine in 1.00 dm 3 of FA 2. moles of Fe 3+ =... mol (vi) The formula of the iron(iii) compound is FeNH 4 (SO 4 ) 2.xH 2 O g of this compound was weighed out and added to excess aqueous acidifi ed potassium iodide. FA 2 was made by making the resulting solution of iodine up to 1.00 dm 3 with distilled water. Use this information and your answer to (v) to calculate the number of moles of water of crystallisation, x, in one mole of the iron(iii) compound. [A r : H, 1.0; N, 14.0; O, 16.0; S, 32.1; Fe, 55.8] x =... [6] [Total: 14]

5 5 2 In this experiment you will determine the enthalpy change, H, for the reaction of zinc with iron(ii) sulfate. Zn(s) + FeSO 4 Fe(s) + ZnSO 4 In order to do this, you will determine the enthalpy changes for the reactions of zinc and iron with aqueous copper(ii) sulfate. Excess of the two metals will be used during the determinations. Then you will use Hess Law to calculate the enthalpy change for the reaction above. FA 4 is zinc, Zn. FA 5 is iron, Fe. FA 6 is mol dm 3 copper(ii) sulfate, CuSO 4. (a) Determination of the enthalpy change for the reaction of zinc, FA 4, with aqueous copper(ii) sulfate, FA 6. Method Support a plastic cup inside the 250 cm 3 beaker. Use the measuring cylinder to transfer 25 cm 3 of FA 6 into the plastic cup. Measure and record the initial temperature of the solution in the space below. Add all the FA 4 from the container to the FA 6 in the plastic cup. Stir constantly until the maximum temperature is reached. Measure and record the maximum temperature. Tilt the cup if necessary to ensure the thermometer bulb is fully immersed. Calculate and record the temperature rise. [3] [Turn over

6 6 (b) Calculations Show your working and appropriate signifi cant fi gures in the fi nal answer to each step of your calculations. (i) Calculate the energy produced during this reaction. [Assume that 4.2 J are needed to raise the temperature of 1.0 cm 3 of solution by 1.0 C.] (ii) Calculate the number of moles of copper(ii) sulfate in 25 cm 3 of FA 6. energy produced =... J moles of CuSO 4 =... mol (iii) Calculate the enthalpy change, in kj mol 1, for the reaction below. Zn(s) + CuSO 4 Cu(s) + ZnSO 4 enthalpy change = kj mol 1 sign value [2]

7 7 (c) Determination of the enthalpy change for the reaction of iron, FA 5, with aqueous copper(ii) sulfate, FA 6. Method Support the second plastic cup inside the beaker. Use the measuring cylinder to transfer 25 cm 3 of FA 6 into the plastic cup. Measure and record the initial temperature of the solution in the space below. Add all the FA 5 from the container to the FA 6 in the plastic cup. Stir constantly until the maximum temperature is reached. Measure and record the maximum temperature. Tilt the cup if necessary to ensure the thermometer bulb is fully immersed. Calculate and record the temperature rise. Keep solution FA 6 for use in Question 3. (d) Calculations Show your working and appropriate signifi cant fi gures in the fi nal answer to each step of your calculations. [2] (i) Calculate the energy produced during this reaction. [Assume that 4.2 J are needed to raise the temperature of 1.0 cm 3 of solution by 1.0 C.] energy produced =... J (ii) Calculate the enthalpy change, in kj mol 1, for the reaction below. Fe(s) + CuSO 4 Cu(s) + FeSO 4 enthalpy change = kj mol 1 sign value [2] [Turn over

8 8 (e) Use your values for the enthalpy changes calculated in (b)(iii) and (d)(ii) to calculate the enthalpy change for the reaction below. Zn(s) + FeSO 4 Fe(s) + ZnSO 4 Show clearly how you obtained your answer by drawing a Hess Law energy cycle. (If you were unable to calculate the enthalpy changes, assume that the value in (b)(iii) is 210 kj mol 1 and the value in (d)(ii) is 144 kj mol 1. Note: these are not the correct values.) enthalpy change = kj mol 1 sign value [2] (f) (i) Calculate the maximum percentage error in the temperature rise in (c). percentage error =... % (ii) Apart from using a more accurately calibrated thermometer, suggest one improvement that could be made to this experiment that would increase the accuracy [2] [Total: 13]

9 9 3 Qualitative Analysis At each stage of any test you are to record details of the following. colour changes seen the formation of any precipitate the solubility of such precipitates in an excess of the reagent added Where gases are released they should be identifi ed by a test, described in the appropriate place in your observations. You should indicate clearly at what stage in a test a change occurs. No additional tests for ions present should be attempted. If any solution is warmed, a boiling tube MUST be used. Rinse and reuse test-tubes and boiling tubes where possible. Where reagents are selected for use in a test, the name or correct formula of the element or compound must be given. [Turn over

10 (a) FA 1, used in Question 1, is an aqueous solution of sodium thiosulfate. FA 6, used in Question 2, is an aqueous solution of copper(ii) sulfate. FA 7 is solid sodium thiosulfate. Carry out the following tests and record your observations in the table below. 10 test (i) Using a spatula, place 2 or 3 crystals of FA 7 into a hard-glass test-tube. Heat gently for several seconds, then observations heat strongly. (ii) To a 1 cm depth of dilute sulfuric acid in a boiling tube, add a few crystals of FA 7. Observe until no further change occurs, then warm the mixture, gently and carefully. (iii) To a 1 cm depth of aqueous potassium iodide in a test-tube, add a few drops of FA 6, aqueous copper(ii) sulfate, then add FA 1, aqueous sodium thiosulfate, to the mixture until no further change occurs. (iv) Using your observations in (ii), complete the equation below by giving the formulae of the other two products. Na 2 S 2 O 3 + H 2 SO 4 Na 2 SO 4 + H 2 O [5]

11 (b) FA 8 and FA 9 are aqueous solutions. Each contains one cation and one anion from those listed on pages 14 and 15. Carry out the tests and record all your observations in the table. For each test, use a 1 cm depth of FA 8 or FA 9 in a test-tube. 11 (i) test Add aqueous sodium hydroxide. observations FA 8 FA 9 (ii) (iii) Add a few drops of aqueous silver nitrate followed by aqueous ammonia. Add aqueous ammonia. (iv) Add an equal depth of dilute sulfuric acid. (v) Add an equal depth of FA 9. (vi) Using your observations, identify three of the ions present in FA 8 and FA 9. Write unknown next to the ion that you cannot identify directly from your observations. ions in FA 8: cation... anion... ions in FA 9: cation... anion... (vii) The unknown ion in (vi) can be identifi ed by elimination, using the lists of ions on pages 14 and 15. Choose one positive test that would confi rm the identity of this ion. Name the reagent(s) you would use and state what you would observe if the test was positive. Do not carry out this test. unknown ion tested for... reagent(s)... observation(s)... [8] [Total: 13]

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14 14 Qualitative Analysis Notes Key: [ppt. = precipitate] 1 Reactions of aqueous cations ion NaOH reaction with NH 3 aluminium, Al 3+ ammonium, NH 4+ barium, Ba 2+ calcium, Ca 2+ chromium(iii), Cr 3+ copper(ii), Cu 2+ iron(ii), Fe 2+ iron(iii), Fe 3+ magnesium, Mg 2+ manganese(ii), Mn 2+ zinc, Zn 2+ white ppt. soluble in excess no ppt. ammonia produced on heating no ppt. (if reagents are pure) white ppt. with high [Ca 2+ ] grey-green ppt. soluble in excess giving dark green solution pale blue ppt. green ppt. turning brown on contact with air red-brown ppt. white ppt. off-white ppt. rapidly turning brown on contact with air white ppt. soluble in excess white ppt. no ppt. no ppt. grey-green ppt. blue ppt. soluble in excess giving dark blue solution green ppt. turning brown on contact with air red-brown ppt. white ppt. off-white ppt. rapidly turning brown on contact with air white ppt. soluble in excess

15 15 2 Reactions of anions ion reaction carbonate, CO 3 2 chloride, Cl bromide, Br iodide, I nitrate, NO 3 nitrite, NO 2 sulfate, 2 SO 4 sulfi te, 2 SO 3 CO 2 liberated by dilute acids gives white ppt. with Ag + (soluble in NH 3 ) gives cream ppt. with Ag + (partially soluble in NH 3 ) gives yellow ppt. with Ag + (insoluble in NH 3 ) NH 3 liberated on heating with OH and Al foil NH 3 liberated on heating with OH and Al foil; NO liberated by dilute acids (colourless NO (pale) brown NO 2 in air) gives white ppt. with Ba 2+ ( dilute strong acids) SO 2 liberated with dilute acids; gives white ppt. with Ba 2+ (soluble in excess dilute strong acids) 3 Tests for gases gas ammonia, NH 3 carbon dioxide, CO 2 chlorine, Cl 2 hydrogen, H 2 oxygen, O 2 sulfur dioxide, SO 2 turns damp red litmus paper blue gives a white ppt. with limewater (ppt. dissolves with excess CO 2 ) bleaches damp litmus paper pops with a lighted splint relights a glowing splint test and test result turns acidifi ed aqueous potassium manganate(vii) from purple to colourless

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Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level

Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level *4147278659* CHEMISTRY 9701/34 Paper 3 Advanced Practical Skills 2 May/June 2015 2 hours Candidates answer